1) Field of the Invention
The present invention relates to a plug-in unit mechanically and electrically connected to a sub-rack having a back plane with a connector and a communication apparatus having such a plug-in unit, and in particular, relates to a technique for realizing electromagnetic shielding and reduction of an influence caused by static electricity in a plug-in unit.
2) Description of the Related Art
With rapid progress of technological innovation, present-day electronic devices are ever on their way to higher performance such as improvement in processing speed and higher-density packaging of electronic components, and accompanying such trends are a rapid increase in radiant quantity of electromagnetic waves from internal circuits of electronic devices and much shorter wavelengths of electromagnetic waves due to higher processing speeds.
Electromagnetic waves can have harmful effects such as malfunctioning and noise contamination of nearby devices, and inoperability and noise contamination of radio broadcasting of TV and radio and radio communications. Also with higher performance, electronic devices have become more sensitive, and malfunctioning by receiving electromagnetic waves radiated by nearby devices and destruction and malfunctioning of electronic components caused by static electricity are more likely to occur. Grave damage such as malfunctioning and destruction caused by these electromagnetic waves and static electricity is a very important challenge to stable operation of electronic devices and demand for electromagnetic shielding and making electronic devices unsusceptible to influences of static electricity is increasing with higher performance of electronic devices.
Thus, for a communication apparatus in which a plurality of plug-in units are installed in a sub-rack device by insertion, a technique (for example, see Patent Document 1) in which, in a plug-in unit, electromagnetic shielding is realized by covering a printed wiring board (hereinafter referred to as a printed board) on which electronic components are mounted with a metallic case has been proposed.
By making electromagnetic waves more unlikely to have an influence to the outside of a plug-in unit with implementation of electromagnetic shielding in the plug-in unit, an influence of electromagnetic waves on electronic devices near the plug-in unit can be eliminated.
Further, a technique (for example, see Patent Document 2) to realize reduction of an influence caused by static electricity by grounding the plug-in units via the sub-rack device has also been proposed.
Here, a communication apparatus 100 having a conventional electromagnetic shielding mechanism will be described with reference to FIG. 8 and FIG. 9. The communication apparatus 100 comprises a sub-rack device 120 adopting a bookshelf form and a plurality of plug-in units 110 mounted in the sub-rack device 120. Numeral 110′ in FIG. 8 and FIG. 9 denotes the plug-in unit 110 before assembled.
The plug-in unit 110 comprises a front panel 111, a printed board 112, and a shield cover 113 so that the front panel 111 covers the front of the printed board 112 and the shield cover 113 covers upper and lower surfaces and both sides of the printed board 112.
Meanwhile, card levers 114 for linking to the shield cover 113 are rotatably placed opposite to each other in upper and lower parts of the front panel 111.
Here, a more detailed description of the plug-in unit 110 will be provided. The printed board 112 of the plug-in unit 110 is inserted into the cylindrical or box-shaped shield cover 113 via arm members 115a and 115b placed to extend along the upper and lower surfaces of the printed board 112, and further the front panel 111 and each of the arm members 115a and 115b of the plug-in unit 110 are linked.
Each of the arm members 115a and 115b comprises plates 115c and 115d sandwiching the printed board 112 with a predetermined space from both sides and a pin 115e that is interposed between the plates 115c and 115d and whose ends are joined to the plates 115c and 115d. 
Then, as shown in FIG. 10(a), a cutout 112a extending toward a top end surface of the printed board 112 is provided at a position corresponding to the pin 115e of the arm member 115a of the printed board 112, and the cutout 112a extending toward a lower end of the printed board 112 is also provided at a position corresponding to the pin 115e of the arm member 115b of the printed board 112.
The pin 115e is inserted into each of these cutouts 112a, and a width W of the cutout 112a is designed to be slightly larger than a diameter D of the pin 115e so that the printed board 112 has little play in an insertion/removal direction (a1-a2 direction) of the sub-rack device of the plug-in unit 110.
A length F of the cutout 112a, on the other hand, is designed to be larger than the diameter D of the pin 115e so that the printed board 112 is freely movable in a vertical direction (b1-b2 direction)
By configuring the plug-in unit 110 such that the printed board 112 is freely movable in the vertical direction, a back plane connector 122 (See FIG. 8) provided in a back plane 121 (See FIG. 8) of the sub-rack device 120 and a plug-in unit connector 116 provided at a rear end of the printed board 112 can be connected without being influenced by variations (tolerance accumulation) of dimensions of components of the plug-in unit 110 and sub-rack device 120.
Here, an insertion sequence of the plug-in unit 110 into the sub-rack device 120 will be described with reference to FIGS. 10(a) to (c). First, as shown in FIG. 10(a), the plug-in unit 110 is moved in an insertion direction (a1 direction) along a lower rail 123 (See FIG. 8) of the sub-rack device 120 in a process of inserting the plug-in unit 110 into the sub-rack device 120.
Then, as shown in FIG. 10(b), the plug-in unit 110 is further inserted into the sub-rack device 120 so that a guide projection 116a of the plug-in unit connector 116 and a guide hole 122a of the back plane connector 122 are brought into contact. If the plug-in unit 110 is further inserted, since the printed board 112 is configured to be freely movable in the vertical direction, the printed board 112 is moved to an appropriate position in the vertical direction (b1-b2 direction) to be plugged in by being guided by end faces of the guide projection 116a and guide hole 112a so that, as shown in FIG. 10(c), the plug-in unit connector 116 can reliably be connected to the back plane connector 122.
Meanwhile, a module called a pig tail in which an optical fiber cable is connected to an optical module in an undetachable state has conventionally been used widely as an optical module mounted in a communication apparatus to switch electric and optical signals (See, for example, Patent Document 3).
FIGS. 11(a) to (c) show a plug-in unit 130 in which an optical module 131 of a conventional pig tail type is mounted. FIG. 11(c) is a C-C′ sectional view of a front portion of the plug-in unit 130 shown in FIG. 11(a). When the optical module 131 to which an optical fiber cable 132 is connected in an undetachable state is used, as shown in FIG. 11(a), the optical module 131 is electrically connected to a printed board 130a by being fastened to the printed board 130a by soldering.
As shown in FIGS. 11(b) and (c), the plug-in unit 130 has an interface 140 for optical fiber connection on a front side. The interface 140 is configured by arranging an optical adapter 141 for connecting and relaying an optical connector to both sides on a swing 142 that is rotatable with respect to a front panel 130b and also connecting another end of the optical fiber cable 132 connected to the optical module 131 for converting electric and optical signals in an undetachable state to the optical adapter 141.
As shown in FIG. 11(c), the conventional plug-in unit 130 in which the optical module 131 of the pig tail type is mounted has a boundary part 133 between the printed board 130a and swing 142 and electromagnetic shielding is thereby realized.
Meanwhile, with ever higher functionality of electronic components, plug-in units in which an optical module [for example, SFP (Small form Factor Pluggable)] obtained by insertably/removably connecting an optical fiber cable and optical module to an optical connector is mounted are nowadays increasingly used.
FIGS. 12(a) and (b) show a plug-in unit 150 in which an SFP 152 is mounted. As shown in FIGS. 12(a) and (b), the plug-in unit 150 has only cases (cages) 153 and electric connectors (not shown) fastened to a printed board 151 for housing the SFPs 152 and the SFP 152 is insertable/removable into/from the case 153. The printed board 151 has four SFPs 152 and cases 153 mounted on the printed board 151.
Then, a front panel 154 of the plug-in unit 150 has an opening (hole) 155 for exposing the SFP 152 to the outside provided at a position corresponding to the SFP 152 and the SFP 152 is thereby mounted in a state in which the SFP 152 is detachable from the front of the plug-in unit 150.
For reasons described above with reference to FIGS. 10(a) to (c), a height (opening length in the vertical direction) of the opening 155 of the front panel 154 is made sufficiently higher (longer) than that (length in the vertical direction) of the SFP 152 also in the plug-in unit 150 to make the printed board 151 freely movable in the vertical direction (b1-b2 direction).
In the plug-in unit 150, as described above, even when a necessity for classification change such as a wavelength of optical signals arises, an end user can cope with the necessity by a simple means of replacing the SFP 152 with another optical module by configuring the SFP 152 to be detachable from the printed board 151 and thus diversified requests to the communication apparatus can be met.
However, as described above with reference to FIG. 11, while the plug-in unit 130 in which the optical module 131 of the pig tail type is mounted can realize electromagnetic shielding and the like, the plug-in unit 150 in which the SFP 152 is detachably mounted has the opening 155 in the front panel 151 and thus has an insufficient boundary of electromagnetic shielding from outside, is likely to direct an influence of electromagnetic waves to the outside and is also susceptible to static electricity.
The present invention has been made in view of the above problems and an object thereof is to make it possible, in a communication apparatus having a sub-rack and a plug-in unit electrically connected to the sub-rack, to detachably mount a module (for example, an optical module) to the plug-in unit while reliably realizing electromagnetic shielding of the plug-in unit. Another object of the present invention is to enable realization of reduction of an influence caused by static electricity.
Patent Document 1: WO 00/074454
Patent Document 2: Japanese Patent Application Laid-Open No. 2002-050887
Patent Document 3: Japanese Patent Application Laid-Open No. 2003-086967